Electric heating unit



May 10, 1949. c. B. CURTISS 2,469,634

ELECTRIC HEATING UNIT Filed April 17, 1947 2. Sheets-Sheet 1 IN VEN TOR.

I Q2 ar/eafil uni/1m ATTORNEY ay 10, 1949. c. B. c uR Tls s 2,469,634

ELECTRIC HEATING UNIT Filed April 17, 1947 2 Sheets-Sheet 2 ATTORNEY elementr Patented May 10, 1949 aceacse ELECTRIIQ EEATENG UNIT Charles B. Curtiss, EBay City, Mich asslgnor in Valley Welding do Eoiicr 00., Bay City, Mich! Y Application April 117,

' 2 Claims.

2 The present invention relates to electric heating units and more particularly to a heating unit 5 or use in garbage disposal apparatus The primary obiect of the invention resides in the precision of an electric heater for garbage 5 the housing P o Will be provided to form dispose?v units and the like, which, while proajunction box structure and facilitate connection tecting she heating element from corrosion of Of the s f the heating le ent w th l ad SllIlOllZlldllEg materials, will at the same time profl c svide electrical msuletimf d good h t radia- Another object of theinvention resides in the tion for drying, heating, or igniting surrounding method of casting the electric heating element in mot l-i l a. sheath of cast alloy in such a manner as to Another object of the invention resides in the Prevent e at f the pour d etal from me1tprovision of an electric heater unit for garbage mg and shorting the electric heating element and disposal units and the like, which will produce #1150 from breaking down h insulation in the dryin temperatures over a relatively long t areaadjacent the cold ends of the electric beanperiod before reaching a maximum temperature, in? element! so that the refuse in the garbage disposal unit Another Object resides in the method of m be considerably dried before final ignition signing the cast alloy sheath for the electnc takes place, then obnoxious odors and smoke are heating element in such a manner that the heateliminated and'other deleterious effects are reof the metal melted for Pouring and the atent duced. heat of fusion during freezing will be absorbed A further object of the invention is to provide by the core for the enlarged housing POrtiOn as a heating unit for garbage disposal units and the wen as the mold thereforlike in which the electric heating element is cast Amther object resides m the method of castin or embedded in a sheath of alloy metal of sufmg m bushing where P l may be i" ficient sectional dimensions to slow the heating chimed thus getting machmabmty and also q period to a gradual heating cycle of from to ed protection cold ends of the heating minutes and extend the drying period during element by absorbmg heat from the poured metal. heating and cooling when the electric power is Other objects and advantages of the invention Suppuedmtermittenfly I 30 will become apparent during the course of the Still a further object of the invention is to profollowing description of the l wherem: I vide a heating element of the above-mentioned .Figure 1 is e1evat.1na1 new garbage type in which the heating unit is cast in an alloy l dlsposal unit ShOWmg a s de Wall portion broken metal, so'that the radiating surface of the sheath away to illustrate the locatm} of the heating umt will be considerably increased so that the term 5 and,the general arrangement -f perature of the heating unit will be only Slightly Figure 2 is a vertical cross sectional view of the greater than the temperature of the sheath thus heating unit showmgln detail the enlarged housincreasing the life of the heating lng portion for receiving the ends of the electrical Another object of the invention is to provide heating element and thus facilitate connection a heating unit for garbage disposal units in o of said ends with lead-in conductors. which the proximity of the sheath or the heat-, Figure 3 is a top eleveiional i of the-beams mg element to the surrounding cast alloy sheath lllllt, portions thereof In Section PO 111115 and the heat conductivity of the cast alloy sheath the general Structure as well as venous causes heat to be taken away from the unit at W and; a faster rate than can be accomplished without 45 Figure 4 is a slde elevfltlonfll Vlew 0f the neatthe castv alloy sheath.

Another object of the invention is to provide an electric heating unit having a heatingelement cast ln'a sheath of cast alloy of sufllcient sectlonal dimensions to increase the heat emissionrate of the sheath with the resultant lowering of temperature of the 'sheath as well asjthe heating Another object or the invention is to provide a 'lieatlns unit of the above-mentioned type which 1947; Serial Noa 742,133

is provided with an enlarged housing portion for receiving so-called cold ends of the electric heating element so that a considerable space be tween the cold ends of the heating element and ,ing unit, showing the circular contour of the major portion thereof and the integral housing portlon projecting axially and radially therefrom.

. In the drawings, attention is first directed to 5 Figure 1 wherein there is shown an adaptation of v the. invention'in the form of a garbage disposal unit, including an insulated casing 5 provided I i v with a receiver chamber 6 disposed above an ash drawer L iG'rate supports 8 are disposed between I. the receiver chamber and the removable drawer I,

3 and a movable grate 9 is disposed above said grate supports and is operable by a shaker bar Il having a projection ii for engaging within an opening in the movable grate 9 so that the to-and-fro movement imparted to the bar l will reciprocate the movable grate 9.

Mounted near the top of the casing I is a flue pipe i2 for conducting the products of combustion to the atmosphere. Also, a hinged cover I! is secured to the open top of the casing 5 to permit the dumping of refuse and garbage into the receiver chamber 6.

The electric heating unit generally designated is mounted-in the receiver chamber 6 and is supported above the grate 9, so as to project upwardly into the receiver chamber 6. As shown in Figure 1, the electric heating unit is supported on the front face of the combustion chamber and is connected to the inner end of a tubular member IS, the outer end of which projects through a sleeve in the wall of the garbage disposal unit 5 and is rigidly connected thereto by means of retaining units (not shown). An outlet box II is affixed to the free end of the tubular support ii for accommodating cable connections with a suitable source of electrical energy.

The electric heater unit [5 is circular in shape to provide an annulus 20, Figures 2, 3, and 4 of round section. The annulus is formed of an alloy metal of proper characteristics for heat dissipation and corrosion resistance.

The type of metal used in the alloy sheath will often be too hard for easy machining, so that to facilitate threading for the connecting support a bushing insert may be cast in the alloy where it may be machined to accommodate the supporting tube or other member. This makes possible the use of the best cast alloy analysis for getting the best operating life of the heating unit.

Formed integral with the annulus 20 is a housing generally designated by the reference character 22, and said housing projects both radially and axially of the axis of the annulus as is shown clearly in Figures 2 to 4 inclusive. The housing is likewise formed of cast alloy and includes an inclined wall portion 23 terminating in a bottom wall 24 extending axially of the annulus (Fig. 2). A top wall 25 of arcuate shape extends axially for a portion of its length and terminates in an inclined wall portion converging in the direction of the lower wall 24. A curved side wall portion 26 connects the bottom and top walls 24 and 25 and provides a rounded front wall-section 26 having an enlarged threaded boss 21 for receiving the threaded inner end of the supporting tube i6 (Figs. 2 and 3).

Thus, an enlarged chamber 30 is formed between the annulus 20 and the tubular support ii to facilitate electrical connections with the electric heating element 3| which is embedded or cast in the annulus. The electric heating element comprises a resistance wire 32 surrounded by steel or heat resistant alloy sheath, the wire is insulated from the sheath by a closely packed layer of magnesium oxide, the resistance wire extending approximately 270 of a circle.

Between the ends of the resistance wire and the connections are two large low-resistance wires in the cold end sections; these are similarly insulated from the sheath and can be threaded on the ends to afford means of connection with the cable conductors extending through ,the tubular support l6 which are also insulated from said support by magnesium oxide or other insulating 7 material.

It will thus be seen that the electric heater element is cast in a sheath of considerable thickness in such a manner that heat will be conducted away from the electric heater element ll at a sreater rate than would occur if the heater element II were spaced from the sheath.

By reason of the annular shape of the heating unit, the radiation area is greatly increased, thus insuring a greater rate of heat emission and a resultant lower temperature of the sheath and therefore of the entire unit including the heating element 3|. The theoretical radiation is expressed in the Stefan-Boltzmann 4th power law of radiation by the formula:

o) Q-K F z where, for example, Q=B. t. u. to be radiated taken as 600 watts or 2047 B. t. u. per hour.

K=constant for east alloy=.157 approx.

=area of radiating surface, taken as 0.4 sq. ft. t =time in hours, taken as 1 hour. T=Absolute temp.: F. of sheath or annulus 20. To=Absolute temp.: "F. of surrounding space.

Then the difference between the temperature of the annulus or sheath and the ambient temperature for various temperatures can be deduced by the above formula, which in the example will be found to be as follows:

Ambient temperature T. 212, 500, 1000, 1500,

Approximate annulus or sheath temperature F.

Diiferential-sheath-ambient temperature F. 694,

Thus, it will be seen that as the ambient temperature is increased, the radiation is more than proportionately increased and hence, the heating element temperature is not equally increased.

All materials radiate heat at elevated temperature at a greater rate than at lower temperatures. Thus at elevated ambient temperatures, at say in the neighborhood of 1500 F., there will be only 101 F. difference between the temperature of the heating unit sheath and the surrounding temperature. This temperature difference is exactly the desired result as it eliminates failure of the heating element due to overheating, since the ambient temperature will seldom, if ever, cause unit temperatures that are excessive.

Method of molding heating unit In the casting of the heating unit I! including the annulus 26 and the housing 22, conventional foundry equipment is employed.

A pattern shaped identical to the heating unit I! and housing 22 is employed for forming the mold cavities in the mold sand in the cope and drag of the mold. After the mold cavity is then formed, the electric heating element II is arranged in a circular manner in the annular portion of the mold and said heating unit is chapleted to assure proper location in the center of the element ii.

The free ends of the electric heating unit are embedded in a dry sand core placed in the housing cavity in the mold so that upon casting, the ends will be protected against high melt temperatures and will not become shorted.

In order to protect the "cold ends of the heating element from failure caused by the heat of the alloy during pouring, it is necessary to design the housing so that the core itself and the 5 surrounding mold will be able to absorb the heat 5 of the metal of the houslxig without raising the temperature of the cold ends dangerously, and gating shall also further this end. Only by this design, and by this method of pouring, can the heating elements be successfully entirely encased in cast alloy.

When the electric heating unit is thus cast from a suitable alloy, the core material is removed from the casting and the casting is fettled in the usual manner. The annular boss 2; may then he threeeieil for receiving the tubular support i8. lBeifosre the tubular support and casting are assembled, suitable electrical connections are made with the terminals of the heating unit, and in euletlng material such es megneslum oxide is peckeal in the chemlzlei' as Well as the tubules l8, anal since the tubular support 4% is clawed outer the electric heating unit he completely exact sealed with the electrical. 57e s mojectimg through the closed. end of .hhe ceectilc heating thus proclucee is then mounted seer the front wall or? the combustion chem as shown ,i e figure It so that the stimulus e11? sheet-h will lie is e plane perpendicular to e tubule? It is to Joe mille stoei that the form of the invention shown disclosed is to be taken as e, preferred ems-cement of the lnvention, and that various changes in the shape, size, and ezri'ene'ement of pests may be resertecl to without departing" from the spiel-t of the invention or the scope Of sulnjolned claims.

Whet claim is:

11. An electrical heating unit, compxlsing a loopshaped ennulep: sheath formed of cast alloy, an insulated electric heating element embedded in said annular sheath, e laterally projecting, hollow housing formed integral with said annular sheath named cavity having a cast in bushing to absorb heat while casting and to permit a threaded bore in the housing, the terminal ends of said electric heating element being received in said housing, a tubular support having one end received in said threaded bore, electrical conductors extending through said tubular support and electrically connected to the terminal ends of seicl heating ele ment Within sale housing, and insulating mew teriel packed in said. housing and tubular sup port, said insulating materiel comprising megnesium oxide.

2. A method of casting a. sheath ei'ouncl an eleetl'lc resistance he? e1 mer t, comprising forming a, mold cavi y the shape of the heating unit desired, moan ctrice? resistance heating element with l lolel. czwltgg :lorming: at relatively large 0 vlty adjacent the cold encls of? the heetne; el ce""ty, placing as core in said last named cavity th the ends of therein and. gating the molten metal will came cavity around ween. said last the melcl cavity flow first into set said heating no 1 The following reieremces in the file of this patent:

ETATES; PATENTS 

